Some quick thoughts, which may or may not be helpful from a gameplay perspective but should be considered from a world perspective:

• Rifling vs. Smoothbore:

The popularity of rifling is only indirectly a result of smokeless powder (or your "force powder" analogy). What smokeless powder really permitted was for reliable and effective metal cartridges to be created. Prior to this, most rifles were muzzle loaded, and you had to physically screw the projectile down the barrel - a laborious and time-consuming task, and what made them actually unpopular for military use. (In-game, this might be represented by rifles having to take an extra turn to reload, but having additional range or a bonus modifier to hit.)

Making an effective breechloading rifle is highly dependent on also being able to reliably produce a metal cartridge that will always fit in the breech, reliably fire, and the bullet fit the rifling no matter where the cartridge or bullet were made. This implies certain metalworking and machining techniques which may have an impact on your world.

• Other things to be aware of.

One thing I don't see mentioned is the primer. In a metal cartridge, the propellant isn't itself detonated by the hammer, but a more-reactive material called the primer is. By definition, the primer is unstable enough that it is unsuitable as a propellant; likewise, the propellant is stable enough that it is unsuitable as a primer. (In weapons prior to modern all-in-one cartridges, the primer sat in a small metal cap which was fitted over a nipple that lead into the firing chamber of the gun; the cap would be replaced after each shot.)

Assuming it's a close analogy of smokeless powder, Force Powder might not be a great primer. That said, your world may have invented the means to produce a viable chemical primer, such as mercury or silver fulminate, which will detonate a main propellant charge of Force Powder.